What is the linguistic origin of the term Shuf'a (preemption)?

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It is said that Shuf'a is derived from Shuf', which relates to a spouse (Zauj), because the preempter joins the purchased share to his individual property, thereby making it double (Yashfa'uhu bihi). It is also said that it is derived from increase (Ziyadah), because the preempter increases the sold property within his ownership.